Regarding an imaging optical system, a structure has been proposed in which a microlens array is disposed on the upper side of pixels; a plurality of pixels is arranged in the lower part of each microlens; and an image from a main lens is further formed on the pixels using the microlens array. In this structure, a group of images having parallaxes can be obtained in the units of pixel blocks. The parallaxes enable performing a refocussing operation based on distance estimation and distance information of a photographic subject. An optical configuration in which an image from a main lens is further formed using a microlens array is called a refocus optical system.
In a configuration in which the refocus optical system is used, the image formed due to each microlens is an image taken by shifting the position of the same photographic subject captured by the adjacent image. Hence, if the images formed due to the microlenses are superimposed, it becomes possible to reconstruct a refocused image focused at an arbitrary specified distance in the image.
In such a refocus optical system, it is important that the central coordinates of the microlens have high accuracy because the image processing superimposes the microlens images with each other by shifting them. Therefore, the central coordinates having a large error may cause the resolution and distance accuracy in the reconstructed image to be reduced.